1. Field of Invention
The present invention relates to the transportation of data through dissimilar communications media. More particularly, the present invention relates to an apparatus and method for transporting data between a remote mobile or fixed terminal device and a host system over multiple, dissimilar communications media. The communications media over which the data is transported include wireless data links, wired data links or a combination of wireless and wired data links which are selected based upon a set of preference metrics.
2. Background Information
The ability to transport data between mobile and/or fixed terminal devices and host computer systems have been generally available for many years. Networks designed to transport this data currently exist in a wide variety of wireless and wired network architectures. Both apparatus and method exists for transporting data through multiple, similar media types as well as the automatic selection of alternate communication paths based upon a plurality of preference metrics.
Often, when multiple networks are available from a common location such as a vehicle, great benefit may be derived by allowing uniform communications through all available networks. Certain networks may perform better for bulk data transfers where another may perform interactive messaging in an optimal fashion. One network may be preferable because of its low cost but an alternate, more expensive network may be acceptable as a backup if the low-cost network is unavailable.
Other examples include U.S. Pat. No. 5,412,375, to WOOD, which discloses a system for selecting one of a plurality of interfaces to a single wireless communications system in accordance with the capabilities of a subscriber unit and the capabilities of a base unit. A list of air interface capabilities of the subscriber unit and the base unit are compared by a controller to determine a compatible interface. As disclosed in WOOD, the plurality of air interfaces include Analog Mobile Phone System (AMPS), Time Division Multiple Access (TDMA) and Code Division Multiple Access (CDMA). While the WOOD system does select from one of a plurality of interfaces which may be applicable for data communication, the routing decision is based on the capabilities of the endpoints rather than the preference metrics of the transporting networks. The endpoint devices, in this case, must be aware of the peculiarities of the wireless environment.
U.S. Pat. No. 5,420,574, to ERICKSON et al., discloses a subscriber unit attached to a trunked mobile radio having a data input. The mobile radio communicates both voice and data message formats over a wireless network to a base station via channels that are allocated by a trunked data controller which is connected to a host network. Channel states and communication parameters are set in accordance with the type of information (e.g., voice or data) that is being transmitted or received. While the ERICKSON et al. system dynamically switches between incompatible message formats without the intervention of the endpoint devices, only a single data path is provided. In addition, the incompatibility of the two alternate paths arises from a difference in message formats rather than the use of independent, incompatible networks.
Further, the transportation of data through alternate, incompatible communications media is a problem that does not have a uniform solution in the art. This problem is exacerbated in wireless communication networks where protocols, timing and other incompatibilities render an otherwise acceptable level of service inadequate. Attempts to provide data links through incompatible networks have suffered from the same obstacles that hindered data communications prior to open standards becoming widely accepted, i.e., proprietary protocols visible to the endpoint terminal devices make the devices inflexible and expensive and the interoperation of similar devices with incompatible networking components is difficult and complex.
Networks may be interconnected by routers which operate at the network level and convey messages between compatible networks. Routers make logical decisions about the pathway through which data is to be directed in the networks based upon a variety of preference metrics. A router is generally implemented as an autonomous device with multiple connections to the networks through which data is to be routed. Routers operate at the network layer and can recognize and manage protocols and multiple connections to networks. Routers usually operate in accordance with the address provided by the particular protocol of the network, and normally provide routing between and through networks utilizing the same network protocol and can route between networks that use different data-link layers, such as Ethernet, Token-Ring, Serial PPP, etc. Another type of router includes two routers loosely-coupled through a protocol-neutral data-link, where the linked routers are considered as a single "virtual" router.
Dissimilar networks may be connected by gateways which are devices that interconnect two or more dissimilar networks. A gateway differs from a router in that the endpoint terminal devices may implement a dissimilar or incompatible protocols. Gateways often perform specific protocol conversions at the layers above the network layer to move data from one type of network to another. In this regard, the Open Systems Interconnection (OSI) model includes seven "layers" to provide communications between heterogeneous (i.e., incompatible) systems. The layers, from lowest to highest, are: the physical layer, the data link layer, the network layer, the transport layer, the session layer, the presentation layer, and the application layer. Each of the layers performs a specific task in transporting data between two or more entities. Such a layered structure is shown in The TCP/IP Companion, by Martin R. Arick, Wiley-QED, pp. 18-19.
U.S. patent application Ser. No. 08/456,860, to DOVIAK et al., for example, discloses a system in which a distant mobile or fixed terminal device transports data through a plurality of wireless network to an endpoint which may or may not implement the same network protocol as the distant device. However, while the DOVIAK et al. system is capable transmitting data over a plurality of dissimilar wireless communications networks, the system does not automatically transmit data through differing ones of a plurality of dissimilar networks in accordance with preference metrics to reach the data-link endpoints. Thus, the system does not automatically provide redundant or alternate pathways through which data may be delivered.
U.S. Pat. No. 5,537,220 to EZUMI et al., discloses a portable facsimile apparatus provided with a capability to communicate over a plurality of communications lines. As disclosed in EZUMI et al., the facsimile machine may communicate over telephone lines or a mobile communication unit. A NCU (controller) is provided within the facsimile machine to discriminate whether the facsimile machine is connected to the telephone line or to the mobile communication unit. The NCU functions to adjust the data rate, and transmitting and receiving signal levels based on which communication system it is communicating. Although this concept may be extended to a generic protocol-neutral data networking environment, the EZUMI et al. system provides for the selection of only one single path to the exclusion of other, possible viable path based solely on which link is plugged into the NCU. Further, the EZUMI et al. system does not switch communication paths within the boundaries of a communication session thereby further limiting its usefulness in a connectionless, packet data environment such as a TCP/IP network.
U.S. Pat. No. 5,602,843, to GRAY, discloses a PBX-based integrated telecommunications system having a wired subsystem connected to wired terminals, and a wireless system for connecting to mobile terminals. A controller is provided which manages base stations and communicates to wireless handsets. When communicating to a handset, the controller determines which base station is in communication with the handset and directs the base station to send packet-based information to that handset. A separate PBX controller is provided to communicate with the wired terminals. The PBX controller includes a proximity sensor to detect wireless handsets such that when a handset is detected in proximity to a wired terminal, messages are forwarded to the wired terminal rather than the wireless handset. While the GRAY system dynamically selects the route to a terminal device based upon a preference metric (wireless proximity), the alternate routing technique does not address transporting data between the same two endpoints. In addition, GRAY provides no means to provide alternate path routing for a terminal device through either the wireless or wired handsets.
U.S. Pat. No. 5,452,471, to LEOPOLD et al., discloses a communication system having a primary and one or more subordinate communication systems. In the illustrated embodiment, the primary communication system is a satellite-base communication system having the widest area of coverage. Each of the satellites within the system defines a cell area which moves as the orbiting satellites move. The secondary and tertiary communications systems are disclosed as terrestrial based, stationary systems having base stations fixed near the surface of the earth (e.g., fixed to a building), where each subordinate system has an increasingly smaller region of coverage. The secondary and tertiary systems include a controller located at a monitoring location within each region. Each of the communications systems includes a link to a central office to enable communications over the public switched telephone network. The LEOPOLD et al. communication systems and mobile subscriber units operate within one frequency spectrum, however, the primary and secondary communication systems operate together by using orthogonal channels to prevent interference. In addition, when communicating with secondary systems, the mobile subscriber unit transmits at a relatively low power such that the primary system will not receive the transmission. The mobile subscriber unit is programmed to utilize the communication system having the smallest area of coverage such that if the subscriber unit has three communications systems available, the subscriber unit will utilize the tertiary communications system (i.e., the system having the smallest area of coverage) based on a designed assumption that the more subordinate the communication system is, the higher the capacity of the system. While the system of LEOPOLD et al. dynamically selects a route based upon a set of preference metrics such that the terminal endpoints are unaware of the routing selection, a common data-link protocol is required throughout all possible associated networks. In addition, the wireless frequencies employed must be derived from a continuous, compatible set of frequencies which prevents the device from selecting among inherently incompatible networks.
Despite the teachings of these prior attempts, users of mobile or fixed wireless data communications are provided with systems of limited capacity and flexibility when routing data through more than one network. In addition, such systems require special hardware and/or software developed for and compatible with the networks, which may require additional training of support personnel and end-users. Further, users of wireless mobile data communication services are provided with only a limited ability to control costs associated with sending and receiving data to and from remote devices, and are limited in their hardware and software design implementations. In previous teachings, the candidate networks must be compatible with one another at either the network or the data-link level. Thus, routing data through inherently incompatible networks such as Cellular Digital Packet Data (CDPD) and Ericsson EDACS is not possible as these are incompatible at both the data-link and network levels. Moreover, known systems do not allow a customer to use existing RF wireless infrastructures, including existing hardware and software, with only minor modifications needed to transport data from a mobile device to a host computer network. In addition, past attempts do not permit wireless data communications in a manner that is transparent to the remote device. Further, prior systems do not provide the flexibility to users such that a plurality of different remote devices may communicate with the wired host network irrespective of the radio infrastructure and transmission protocol employed. Such features, without the above-noted drawbacks, would be highly desirable to provide flexibility and ease of use, and to give users of portable data devices greater control over their hardware and software design.